It’s been a pretty chaotic week in the zoonotic SARS-CoV-2 world, with a lot of attention being paid to hamsters in Hong Kong and deer in Canada.
However, one issue that’s gotten less attention is the need to keep up with this virus as it changes, through serial waves and new variants, and to remember the limitations of our knowledge. I do a lot of talks and interviews about SARS-CoV-2 and often get into discussions of which species are susceptible and which ones aren’t, but there are always some important disclaimers I try to include. One big one is “but, what we know about SARS-CoV-2 in animals almost all pre-dates Omicron. Most of it pre-dates Delta, and even Alpha.”
Why is that important?
If we look at what we know about SARS-CoV-2 in some species, it’s based on experimental models, where animals were deliberately infected using the virus strain that was available at the time. Through those studies, we’ve concluded that species such as cattle and pigs are poorly susceptible, and SARS-CoV-2 exposure of such livestock is unlikely to be of relevance for either human or animal health (though people should still avoid contact even with these animals if they’re sick). Most of those studies were done with the original (pre-variant) SARS-CoV-2 strain. They were really important studies, but the virus strains that were used aren’t relevant anymore. The concern is that it can lead us to say “We’re good here – we don’t need to worry about that species, so we won’t do any more surveillance or future studies”.
Does that matter?
Maybe. The major SARS-CoV-2 variants like Delta and Omicron behave very differently in people from the original strain, and in most cases we don’t know if the same is true in animals or not. It’s a risky approach to assume they won’t behave differently in animals as well.
Can new variants behave differently in animals?
Yes, and susceptibility to variants can be affected both ways. Earlier in the pandemic, it was shown that a species of mice that wasn’t susceptible to the original SARS-CoV-2 strain was susceptible to the Beta and Gamma variants. They then showed that the same didn’t apply to Delta.
More recently, reduced susceptibility to Omicron was reported in mice and hamsters. A study from a few days ago reported that Omicron doesn’t readily infect Syrian hamsters, a species that is susceptible to other strains.
These studies show the need to investigate the impact of each variant on each species.
None of this is meant to say that the sky is falling and we’re going to see a massive change in species susceptibility or emergence of new animal issues with SARS-CoV-2. However, it means that we can’t be over-confident based on what’s been seen in the past. We have to remember the limitations of our knowledge and make sure that we try to keep up with changes in this virus rather than rely on outdated information.
We need to keep working to identify (and ideally head off) issues, rather than using the typical reactionary approach, where we wait until there’s clear evidence of a problem before we act. The need for more work includes a range of studies (field and experimental) and species (including some species that haven’t been investigated since those very early studies). It also requires motivation and financial support, which has been lacking in most areas. The amount of funding I’ve had for SARS-CoV-2 surveillance is basically the equivalent to a few remdesivir treatment courses. We’ve gotten good stuff done, but it’s on a shoestring budget and with little coordinating assistance, unlike some other jurisdictions where public health has integrated animal surveillance studies into their COVID-19 response plans, which is really the way to go.
We’re still at a time when SARS-CoV-2 is screaming through the human population, but that stage will end. Eventually we’ll reach a point where the biggest pool of potentially susceptible individuals is animals, and the relevance of animal reservoirs and animal populations as sources of variants will increase. We’re better off figuring out the issues now (as much as we can) rather than continuing to try to play catch-up later.